The invention relates to improvements in methods of and in apparatus or machines for grinding the exposed surfaces of protuberances on rotary workpieces, particularly for grinding the exposed surfaces of out-of-round portions (such as cams or cam lobes) of elongated rotary workpieces in the form of camshafts or the like. For the sake of simplicity, the following description will refer, primarily or exclusively, to protuberances in the form of cams and to workpieces in the form of camshafts. It is to be understood, however, that the invention can be practiced with equal or similar advantage for the grinding of protuberances other than cams or cam lobes on elongated camshafts.
It is well known to grind the cams of a camshaft by rotating the camshaft about its longitudinal axis and by moving a grinding implement, such as an endless abrasive belt or a grinding wheel, radially of and toward the peripheral surface of a cam on the rotating camshaft. The extent of movement of the implement toward the axis of the rotating camshaft determines the quantity of material which is removed from, and hence the ultimate shape or contour of, the treated cam. The machine which is used for the practice of such conventional grinding method employs a work holder which is normally provided with a headstock and a tailstock for the end portions of the camshaft to be treated, and the machine uses a motor or the like to rotate the properly held workpiece about its longitudinal axis. The material removing implement of the tool in such conventional grinding machine is or can be an endless abrasive belt which is caused to perform a circulatory movement, or a grinding wheel which is driven to rotate about its own axis during material removing engagement with the peripheral surface of a single cam or with the peripheral surface of a selected cam on the rotating camshaft. The base or bed of the grinding machine is provided with guides in the form of ways, tracks or rails which confine the tool to movements substantially radially of the axis of the rotating camshaft. The motor which serves to move the tool along the guide means is controlled, numerically or otherwise, to ensure that the wheel or the belt will remove a requisite quantity of material from the rotating cam, i.e., to ensure that the finished cam will assume a desired contour such as is necessary when the camshaft is used in a motor vehicle to control the movements of valves or for any other purpose where the cam or cams of the camshaft must control the movements of one or more followers or like parts with a high or very high degree of accuracy.
Certain presently known grinding machines employ relatively large grinding wheels which are driven to rotate about their own axes and are simultaneously moved radially or substantially radially of the axis of the rotating workpiece to remove material from the periphery of a cam. The angular movements of the rotating camshaft are synchronized with radial movements of the grinding wheel to thus ensure that the rate of material removal from different portions of a cam blank takes place with a view to produce a finished cam whose contour matches a desired or required configuration.
German patent application Serial No. 40 29 129 A1 of Eckert (published Mar. 3, 1992) discloses a grinding machine wherein a cam of the rotating camshaft is treated by an endless flexible abrasive belt mounted on a carriage for movement radially of the axis of the camshaft which is supported in a holder on the base of the machine frame. An advantage of the grinding machine of Eckert is that its belt can remove material from concave (receding) portions of peripheral surfaces of cams on the rotating camshaft.
A drawback of conventional methods and machines, irrespective of whether they employ material removing implements in the form of grinding wheels or abrasive belts, is that their operation is reasonably economical (i.e., that they can finish a relatively large number of camshafts per unit of time) only as long as they are called upon to grind a single cam at a time. Furthermore, the rate of material removal from a single cam also depends upon a number of additional factors such as the nature of the material of the cam, the characteristics of the material removing implement which is being used to carry out the grinding operation and/or the desired quality of the finished cam, i.e., the finish of the peripheral surface as well as the extent of deviation of the ultimate contour from an optimal or ideal contour. At any rate, even if a conventional machine is designed to grind a single cam at a time, its output cannot be increased at will even if all of the aforediscussed requirements (including the desired quality of the ultimate product, the material of the workpiece and the characteristics of the material removing implement) are fully met. The situation is further aggravated if a conventional machine is to be used to simultaneously treat two or more cams on a common camshaft, especially if the cams are angularly offset relative to each other in the direction of rotation of the camshaft about its longitudinal axis. Machines of such character are disclosed, for example, in U.S. Pat. No. 4,833,834 (granted May 30, 1989 to Patterson et al. for "Camshaft belt grinder") and in U.S. Pat. No. 4,945,683 (granted Aug. 7, 1990 to Phillips for "Abrasive belt grinding machine"). The disclosures of all of the above enumerated publications are incorporated herein by reference.